Introduction
Metered dose inhalers have been conventionally used to control chronic obstructive pulmonary disease symptoms. However, due to the difficulties associated with metered-dose inhalers and the ban on chlorofluorocarbons (a chemical used as the propellant in metered-dose inhalers), new inhalation devices have been developed. Often patients who use metered dose inhalers develop a poor inhalational or erroneous technique. In patients using dry powder inhalers, errors or poor techniques are rarely seen. Dry powder inhalers are easier to use and cause fewer irritating effects. Studies have shown similar bronchodilation (dilation of the airways due to relaxation of surrounding muscles) effects to that of a metered dose inhaler, and only a few patients develop poor inhalation techniques on long-term use. Dry powder inhalers are unsuitable for patients who take large doses of steroids through inhalation routes and in inhalers with spacers.
What Are Dry Powder Inhalers?
Dry powder inhalers are devices used to deliver medicine to the lungs when a patient breathes in through the device. The patient's inward breath activates the drug. Unlike a metered dose inhaler, the dry powder inhaler does not require fuel to shove the medicine into the patient's lungs.
The dry powder inhalers are available in a single dose and multiple dose devices containing up to 200 doses.
How Does the Dry Powder Inhaler Deliver Medicine to the Lungs?
Though dry powder inhalers appear to be simple, they are sophisticated devices. The act of breathing delivers functional medicine to the lungs. The drugs are compacted in the device. Inhalation provides energy to break up the compacted medicine and delivers it to the lungs. The process is known as de-agglomeration. The drugs in the device are blended with carriers like lactose, which prevents clumping and increases the flowability. The airflow generates shear forces and turbulence when the patient inhales through a dry powder inhaler. The powder containing the drug is released from the inhaler. Once it reaches the airway, the larger carrier particles like lactose are separated from the drug particles in the oropharynx and are swallowed. The drug particles are carried deep into the lungs. The quantity of medicine deposited in the lungs depends upon two factors:
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The patient's inspiratory effort is the force with which the patient breathes in air.
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Properties and working of the device (mouthpiece structure, flow, and flow resistance).
To achieve maximum drug delivery to the lungs, several modifications and developments have been made in the drug formulation and design of the dry powder inhaler. Grids, lacunas, and swirl chambers are added to the inhaler to present varying degrees of resistance to airflow. Hence, depending on the drug formulation and the device's design, differences in flow rate and pressure drop (the difference in pressure between two points of a fluid-carrying network) are seen. Generally speaking, the flow rate of drugs through a dry powder inhaler is directly proportional to the square of the pressure drop created by the patient. Here the constant of proportionality is the device resistance.
What Is the Significance of Dry Powder Inhalers in Chronic Obstructive Pulmonary Disease?
Chronic obstructive pulmonary disease is one of the leading causes of death worldwide. Furthermore, it contributes to a significant burden in the economy associated with hospital admissions during an exacerbation, thus reducing productivity. An important treatment modality for controlling the disease is administering medications through breath-activated dry powder inhalers. For effective delivery of the drugs to the lungs, the patient should breathe in with sufficient force to counter the internal resistance of the dry powder inhaler device, leading to the breaking down of aggregated drug powder.
The maximum airflow rate obtained during the process of inspiration is referred to as the peak inspiratory flow rate (PIFR). The flow rate is measured based on the inhaler device's internal resistance (resistance offered to airflow). Therefore, it depends upon the shape and design of the device.
Several dry powder inhalers require a peak inspiratory flow rate greater than 60 liters per minute for adequate drug deposition into the lungs. However, some devices work efficiently with a peak inspiratory flow rate of 30 liters per minute. Factors determining the peak inspiratory flow rate in chronic obstructive pulmonary disease patients are as follows.
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Gender - Females have a reduced peak inspiratory flow rate.
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Age - PIFR decreases with age.
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Reduced At the time of COPD (chronic obstructive pulmonary disease) exacerbations.
What Drugs Are Used in Dry Powder Inhalers for Chronic Obstructive Pulmonary Disease?
Drugs used for chronic obstructive pulmonary disease in dry powder inhalers are steroids, bronchodilators, or a combination.
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Steroids: Budesonide, Fluticasone, Mometasone.
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Bronchodilators: Albuterol, Salmeterol, Tiotropium.
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Combination Drugs: Fluticasone-Salmeterol, Fluticasone-Vilanterol.
Dry powder inhalers depend upon the airflow force the patient breathes in. Therefore, the age and gender of the patients with chronic obstructive pulmonary disease are more important determinants of the airflow rate through the dry powder inhalers than the extent of airway obstruction. Several studies have shown that patients in different age groups and with varying disease severity can generate sufficient airflow through the dry powder inhaler to deliver the medication to lower airways to reach the lungs.
Conclusion
Several devices are available to deliver drugs efficiently and successfully to a patient's lungs. However, the complex physics involved in drug delivery and the myriad of devices available make it difficult for physicians to choose the right device for their patients. The dry powder inhalers, if used correctly, will provide symptom relief for patients with chronic obstructive pulmonary disease. The major drawback of inhalation therapy is the need for more patient cooperation and competence with the inhalation device. There is no single best device for a particular patient, and the choice should be made keeping in mind the parameters important to the users, like the size of the inhaler, portability, and environmental factors. These factors are usually less important medically but are considered the defining factor for the success of the treatment. Most patients can use nebulizers, metered dose inhalers, and high and low-resistance dry powder inhalers.
